​To determine whether Drug Z lowers blood pressure, it is necessary to demonstrate that an experimental group, which has been given Drug Z, will have lower blood pressure than a comparison group, which has been given

A) ​a higher dose of Drug Z.
B) ​a lower dose of Drug Z.
C) ​a placebo treatment.
D) ​no treatment at all.

The most effective way to determine if Drug Z lowers blood pressure is to compare it with a placebo treatment. A placebo is an inactive substance or treatment that is given to the comparison group, which makes them believe that they are receiving the real treatment. By comparing the blood pressure of the experimental group and the comparison group, we can determine the effects of Drug Z on blood pressure without any confounding variables. Comparing different doses of Drug Z or giving no treatment at all will not provide this level of control.